1. Field of the Invention
The present invention relates to a wrapping material for foods such as hamburger and OKONOMIYAKI, which can be heated with its contents in a microwave.
2. Description of the Related Arts
In recent years, as the diversification of foods proceeds, fast foods such as hamburgers, hot dogs and OKONOMIYAKI (a thin, flat cake of unsweetened butter fried with bits of vegetables and meats) have been widely spreading. These foods are taken in restaurants as they are cooked warm, or foods are consumed warm in resturants or then eaten outside or at home. When people eat such takeouts at home, they usually rewarm the takeouts in their microwaves. In any case these takeouts are wrapped with impermeable sheets that do not allow water or oil to penetrate, in order to prevent dirtying the customer's hands and clothes with oozing sauce, ketchup or the like. Sometimes they are additionally placed in styrofoam or like containers.
Available impermeable sheets for this purpose are laminates of tissue/polyethylene or polypropylene film, tissue/aluminum foil, tissue/aluminum foil/polyethylene film, and the like. These sheets are formed into bags as they are, partly backed with an absorbent sheet, partly replaced by a permeable water-proof film or perforated film, or by like means.
Where warm foods just after being cooked, such as hamburger, are wrapped with these impermeable sheets, there occurs a problem wherein excess vapor inside the wrap condenses on the inside surface and the water drops formed are absorbed into the food contained therein, thereby impairing the taste or changing the shape. If the foods are wrapped after being cooled, vapor will generate upon heating in microwave and then condense to produce similar results. Where the inside is covered with an absorbent sheet, the condensed water drops are absorbed in the sheet to make it wet, whereby the wet sheet touches the food to moisten and impair its taste. Furthermore, absorbent sheets have little heat insulation ability and the foods contained therein, when taken out, cool in a short time.
With bags partly comprised of a permeable water-proof film or a perforated film are used, the effect of removing vapor is not sufficient and dew drops still tend to form inside the film and cause similar problems. In addition, impermeable water-proof sheets are very expensive and perforated films have a drawback of leakage of sauce or ketchup through the holes. The use of these films for part of a bag has another drawback of increasing the manufacturing cost due to complex manufacturing processes and high percentage defect caused by poor adhesion or the like.